1. Field of the Invention
The present invention pertains to the field of printed circuit board (PCB) design. More particularly, this invention relates to the art of removing acid traps from a hatched fill in a printed circuit board design.
2. Background
Printed circuit board (PCB) designers are under intense pressure to decrease design cycle times while simultaneously increasing the functionality and quality of design prototypes that are used to drive production. That is, a PCB prototype should not include features that are unusually difficult to mass produce and hence likely to decrease the yield rate, or percentage of usable PCBs. Time and money may be wasted if a prototype has to be altered to improve manufacturability. Predicting and correcting problems at the design stage is often much more efficient than correcting problems at a later stage.
One potential manufacturing problem comes from irregular circuit geometries that are often referred to as "acid traps" or "slivers." For instance, if the conductive material on a PCB includes sharp angles or small openings, mass producing the PCB may be unusually difficult, resulting in a low yield rate. For example, in a detractive manufacturing process, a PCB begins with a layer of conductive material, such as copper, covering a surface of the board. The board is dipped in an acid bath and rinsed to remove unwanted conductive material, leaving behind the circuit design. If the design includes sharp angles or small openings forming irregular pockets, the acid may not be rinsed entirely out of the irregular pockets on every board. In which case, the acid may continue to corrode the conductor, leaving behind open circuits and/or conductive residue which may deposit elsewhere on the board, potentially causing short circuits.
Sharp angles that form irregular pockets can also cause manufacturing problems, such as short circuits, in an additive manufacturing processes in which conductive material is added rather than removed. For instance, conductive traces may run together at sharp angles or small openings. Furthermore, where traces run together, a drop of liquefied conductive material may flow into surrounding areas or traces.
Acid traps and slivers, generically referred to herein as acid traps, are particularly troublesome in hatched fill areas of printed circuit boards. A hatched fill is an area of a printed circuit board that is filled with a cross-hatched pattern of conductive material for any of a variety of reasons, such as to provide shielding, a ground plan, etc. If the boundaries of a hatched fill area are irregular with respect to the fill pattern within the boundary, acid traps are almost certain to occur. For this reason, many designers may be reluctant to use hatched fills, even though hatched fills can be very useful, because hatched fills often have to be altered at the prototype stage to improve manufacturability. Alterations may involve manually identifying and filling in potential problem areas on a design; a process that can be tedious and error ridden.
Thus, a need exists for a method and apparatus for automatically removing acid traps from a hatched fill in a printed circuit board design.